This invention relates to mailers and mailer window patches adhered thereto which resist delamination and picking at temperatures encountered in fuser rolls of laser printers, and in particular, to the use of heat and moisture resistant adhesives for adhering transparent mailer windows to mailer substrates.
Nonimpact printers are finding increasing use and acceptance in a variety of businesses. In particular, the use of nonimpact printers, such as laser printers, for the printing of labels, business forms, and mailers is growing rapidly. Such printers operate by turning on and off a computer-controlled laser beam of light in a specific pattern onto an image cylinder or drum to form a latent image of positive and negative static charges.
As the image cylinder is rotated, toner particles from a toner cartridge are deposited on the image areas on the cylinder and held there by the static charges. As the image cylinder continues to rotate, the now visible toner image on the cylinder is then transferred to paper which has been statically charged to attract the toner particles and has the correct level of conductivity required. A corona wire positioned adjacent the image cylinder then erases the cylinder so that a new cycle may begin.
Typically, the toner image on the paper is then fused by passing the paper through a pair of rolls which apply both heat and pressure to the paper. This fusing of the thermoplastic binder which accompanies the toner by the application of heat and pressure is designed to bond the toner particles permanently to the paper. Fusing temperatures of from 400.degree. to about 450.degree. F. may be encountered by the paper in the fusing rolls.
One disadvantage of using nonimpact printing devices such as laser printers has been the difficulty of printing variable information on envelopes or mailers. Previously, when prior art natural dry gum or hot melt adhesives heretofore found on the flaps of envelopes or on the marginal portions of mailers encountered the high temperatures in the fusing rolls of such printers, the adhesives would soften, become tacky, and then adhere to both the fuser rolls and prematurely to the paper substrate of the envelope or mailer. Obviously, such a result was unacceptable as it damaged both the printer and the envelope or mailer.
There have been several attempts in the art to solve this problem. For example, Steidinger, U.S. Pat. Nos. 4,754,915 and 4,889,278, teaches the application of glue or adhesive to a mailer construction after printing in a laser printer, or alternatively, applying glue or adhesive in a manner such that the glue or adhesive is covered and protected by another portion of the mailer so that it does not directly encounter the fuser rolls of a laser printer.
Chen et al, U.S. Pat. Nos. 4,784,317 and 4,898,323, teach the application of a heat resistant, water or moisture activated adhesive to the marginal portions of a mailer to avoid adhesive activation problems in the fuser rolls of a laser printer. Alternatively, Chen et al teach the application of a pressure sensitive adhesive and then covering the adhesive with a protective release liner for passage through a laser printer.
Schmidt, U.S. Pat. Nos. 4,944,449 and 4,944,450, teach the application of a remoistenable adhesive along certain marginal portions of a mailer construction after the construction has been printed in a laser printer. Dicker, U.S. Pat. No. 4,951,864, teaches the application of a water activatable, heat resistant adhesive to the marginal edges of a mailer construction which is imaged in a laser printer.
None of the prior art, however, addresses the distinct problem of printing window-containing mailers which include a transparent polymeric or glassine patch overlying a die-cut opening in the mailer, imaged in nonimpact printers such as laser printers. Use of conventional natural dry gum or hot melt adhesives to secure the window patches results in softening of the adhesives in the fuser rolls, causing delamination of the windows (known in the art as "picking"). Transfer of the adhesive onto the fuser rolls may also occur. Additionally, there may be a build up of static charges on such fuser rolls which then have an affinity for many polymeric films and exacerbate the picking problem.
While it may be possible to print the inside of a mailer prior to attaching a transparent window patch thereto, such is impractical. Users of mailers need to be able to print variable information on the mailer. Equipment with the capability to place an adhesive bead around a die cut area accurately and then apply a transparent patch is typically too complex and expensive for such users.
The use of transparent polymeric films as window patches has increased because the automated sorting equipment used by the U.S. Postal Service can accurately scan through such polymers more readily than glassine. However, because of the essentially nonporous nature of such polymeric films, conventional adhesives heretofore used do not adhere well to polymeric surfaces. The adherence problem is compounded where the bond between window patch and mailer substrate is subjected to the elevated temperatures encountered in the fuser rolls of laser printers.
Accordingly, the need still exists in the art for envelopes and mailers having transparent window patches therein which resist picking at temperatures encountered in the fuser rolls of laser printers, and for a heat and moisture resistant adhesive which provide strong bonds between a window patch and mailer or envelope substrate.